The following description contains references to certain compositions, articles, and methods. These references should not necessarily be construed as an admission that such compositions, articles and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that the below-described subject matter does not qualify as “prior art” against the claimed invention.
Cemented carbide bodies are manufactured according to powder metallurgical methods including milling, pressing and sintering. The milling operation is an intensive mechanical milling in mills of different sizes and with the aid of milling bodies. The milling time is of the order of several hours up to days. Such processing is believed to be necessary in order to obtain a uniform distribution of the binder phase in the milled mixture, but it results in a wide WC grain size distribution.
In U.S. Pat. Nos. 5,505,902 and 5,529,804 methods of making cemented carbide are disclosed according to which the milling is essentially excluded. Instead, in order to obtain a uniform distribution of the binder phase in the powder mixture the hard constituent grains are precoated with the binder phase, the mixture is further wet mixed with pressing agent dried, pressed and sintered. In the first mentioned patent the coating is made by a SOL-GEL method and in the second a polyol is used.
Swedish patent application 9703738-6 discloses a method of producing submicron metal composite materials such as cemented carbide. Instead of precoating the WC grains with binder phase, the WC grains are precoated with elements inhibiting grain growth, such as Cr and V.
U.S. Pat. No. 5,624,766 discloses a coated cemented carbide insert with a bimodal distribution of WC grain size, with WC grains in two groups: 0.1-1 μm and 3-10 μm. The insert according to this patent is produced with conventional milling and sintering techniques resulting in an inevitable broadening of the WC grain size distribution during milling and grain growth during sintering.
WO 98/03690 discloses a coated cemented carbide insert with a bimodal distribution of WC grain size, with WC grains in two groups: 0-1.5 μm and 2.56-6.0 μm. Although there is no milling, a certain amount of grain growth takes place in the sintering step.